In order to control and monitor the operation of gas turbines, it is necessary to measure and/or to determine in the combustion chambers of the gas turbines the high temperatures occurring there for the hot gases. Because of the high temperatures and the rugged environment at the measurement site, such a temperature measurement confronts the measurement technology with virtually insurmountable difficulties. One possibility of circumventing these difficulties consists in measuring the temperature of the gases at a cooler point of the machine located further downstream and using the measured data to derive temperatures in the combustion chamber on the basis of a machine model. However, it is disadvantageous in this case that there is only a very indirect and time-delayed relationship between the actually measured temperatures and those to be determined.
Another possibility consists in conducting the temperature measurement by using, for example, thermocouples made from special metals such as platinum and platinum-rhodium which withstand the hot gas temperatures occurring in the combustion chamber and can thereby be used directly in the combustion chamber for measurement purposes. However, the high costs which occur from using such metals, in particular in the case of the use of several measurement sites, constitute a disadvantage here.
It has therefore already been proposed in GB-A-2 100 003 to make use for temperature measurement in aircraft turbines of combined thermocouple arrangements which operate on two staggered temperature levels and comprise a short high-temperature thermocouple, arranged between the two temperature levels and made from platinum/platinum-rhodium, for the first high temperature level, and a compensation thermocouple, which has a lower load bearing capacity and is made from alumel/chromel, for the second, lower temperature level. The actual temperature of the first temperature level can then be determined computationally from the measured data of the two thermocouples. However, the savings made on wire length for the high-temperature thermocouple are bought at the expense of a complicated design of the measurement probe and by the doubling of the number of measurements.